The invention relates to a control device of a transmission ratio between a traction means and a wheel set rotatable about a wheel axle and including at least two wheel blades alternatively wrapped around by the traction means, wherein at least one of the wheel blades is composed of several independently adjustable wheel rim segments, wherein the adjustment of the wheel rim segments in relation to a fixed plane (“plane of alignment”) in which the traction means wraps around the wheel set is effected by the control device in a direction substantially transverse to the plane of alignment, wherein the control device comprises at least one electrically actuatable control element, in particular a actuator.
A control device of this type is, for instance, described in US 2002/0084618 A1.
Various solution principles are known for actuating changeable transmissions with wheel rim segments.
There, mechanical control elements each associated to a wheel rim segment are moved one by one by running onto a stationary switch or ramp so as to enforce their movements, and hence movement of the wheel rim segments. Such control elements may, for instance, be designed as eccentrics moving the segment into and out of the operating range, or of wedges causing such movement by axial displacement.
Likewise known are solutions in which the movements of all wheel segments are simultaneously triggered by a central control device rotationally decoupled from the stationary actuator. In those cases, the control members are preloaded by an energy accumulator, in particular a spring element, and the wheel segments are prevented from their adjustment movements until the correct shifting moment has been reached, whereupon the adjustment will take place under the action of the energy accumulator.
Some solutions are based on the principle of temporarily moving the divided, segmented or interrupted sprockets only during the shifting operation itself in order “to bring” the chain to the next-larger or next-smaller diameter. Such solutions are, for instance, described in U.S. Pat. No. 4,127,038 or U.S. Pat. No. 4,580,997. There, the chain is brought into alignment with the consecutive chain blade by pivoting in or axially moving the larger or smaller adjacent chain blade sector. The alignment of the chain thus changes with a change of the transmission ratio.
CH 617 992 A5 discloses a principle by which the chain segments are gradually brought into alignment with the chain. The chain blade segments are individually mounted on a corotating device by means of pins. This enables a smaller construction. It will thus be basically possible to construct derailleur gears that provide the entire spectrum of transmission ratios on a single axis.
In all of the presently known principles, the adjustment of the wheel rim segments is accomplished by the mechanical power transmission between a part of the control device corotating with the wheel rim segments and a non-corotating part of the control device. The non-corotating part is, for instance, fastened to the bicycle frame and performs an adjustment stroke that causes the adjustment of the wheel rim segments during the rotation by the appropriate cooperation with a corotating part of the control device. This involves the drawback of causing constant mechanical contact, and hence friction, during the operation of the system. In addition to undesired stress and wear, this will also lead to the generation or noise and require the observance of exact manufacturing tolerances and high adjustment expenditures during assembling. Such principles are thus expensive in practice, rendering assembly difficult.
From the prior art, both manually operable control devices and electrically operable control devices are known. An electrically operable control device for a transmission gear with segmented sprockets is, for instance, described in US 2202/0084618 A1, which, however, involves the same drawbacks in terms of power transmission from a stationary to a corotating part of the control device as explained above in connection with manually operable control devices. Moreover, electric control devices for conventional derailleur gears are known, yet also these have the disadvantage that a derailleur mounted to the stationary part (e.g. bicycle frame) enforces a change of the traction medium between the undivided wheel blades. Here too, an interface between rotating and stationary units is provided.